Some historians dismiss the Popol Vuh as a contaminated document, containing not only ancient Mayan mythology but also contemporary Spanish Catholic influences. The discovery of the panels establishes key portions of the stories as genuinely Mayan. “We can now extend the authenticity of the creation myth back another 1,000 years,” Hansen says.
The Popol Vuh was first written down in the 16th Century. One reason that scholars had previously viewed it as a "contaminated" document is that portions of it were seemingly inspired by Judeo-Christian theology which didn't arrive in the new world until after Columbus.